The present invention relates to photoanalysis apparatus and more particularly to photoresponsive apparatus for detecting various characteristics of small particles such as blood cells.
There is a great need for accurate analysis of the characteristics of groups of small particles. A particularly important field for such analysis is in medical research and diagnosis where, for example, blood cells and other biological cells must be analyzed.
Various systems have been developed for analyzing groups of small particles such as blood cells. In one system the analysis is accomplished optically by entraining the particles such as blood cells in a very thin stream of liquid and passing the stream containing the particles through an optical scanning station. A photo-optical detecting device is arranged to detect the optical reaction of each particle to illumination from a beam of light.
In photoanalysis systems as described above it has been recognized that the light scattering effect and the fluorescent effect produced by particles in the stream passing through the optical scanning station varies according to different characteristics of the particles, including such factors as particle size, refractive index, particle staining and composition. It has also been found that the beam of light passing through the liquid stream forms a light pattern, the light pattern being different for the stream with and without particles as well as for different size and type particles. Additionally, the thin stream of liquid produces light reflections at various interfaces such as the air/water or glass/water interface. The reflections, light pattern and light beam all are coupled to a photodetector which converts the light signals received to electrical signals which are analyzed to determine presence of a particle and particle characteristics.
The light pattern and light reflections developed at the photodetector when no particle passes through the light beam may have a rather high intensity. This high intensity light will create noise in the electrical signals produced by the photodetector. To eliminate the noise the photodetector sensitivity may be decreased.
The variation in the light reflection and light pattern formed at the detector in response to passage of a particle through the light beam may not be very great so that the resultant variation and electrical output signal from the photodetector may be small. Because of the high noise level due to the background light and the reduced photodetector sensitivity, it may be difficult to detect particles or to accurately detect and identify various particle characteristics. It is therefore desirable to eliminate or minimize, to the greatest extent possible, the light patterns and light reflections received by the photodetector when there are no particles in the flow stream passing through the light beam. That is, to minimize the background light.